somehow to pass context

[tunnckoCore]

To the each function? Actually it would be same for all in stack.

function fn1 (cb) {
  assert.equal(this.hello, 'world')
  this.foo = 'foo'
  cb(null, 1)
}

function fn2 (cb) {
  assert.equal(this.foo, 'foo')
  assert.equal(this.hello, 'world')
  this.bar = 'bar'
  cb(null, 2)
}

function fn3 (cb) {
  assert.equal(this.bar, 'bar')
  assert.equal(this.hello, 'world')
  cb(null, 3)
}

var seriesDone = bach.series(fn1, fn2, fn3)
seriesDone({hello: 'world'}, function (err, res) {
  console.log(res)
  //=> [1, 2, 3]
})

like middleware/plugin stack

[phated]

bach is all about function composition. The above can be achieved like

function fn1 (cb) {
  assert.equal(this.hello, 'world')
  this.foo = 'foo'
  cb(null, 1)
}

function fn2 (cb) {
  assert.equal(this.foo, 'foo')
  assert.equal(this.hello, 'world')
  this.bar = 'bar'
  cb(null, 2)
}

function fn3 (cb) {
  assert.equal(this.bar, 'bar')
  assert.equal(this.hello, 'world')
  cb(null, 3)
}

var ctx = {hello: 'world'};
var seriesDone = bach.series(fn1.bind(ctx), fn2.bind(ctx), fn3.bind(ctx))
series(function (err, res) {
  console.log(res)
  //=> [1, 2, 3]
})

It is a little more verbose, but being verbose and explicit never hurt anyone. It also allows you to avoid passing context to some functions if you want.